Astable transistor multivibrator frequency divider

ABSTRACT

A frequency divider is formed by an astable transistorized multivibrator of symmetrical construction comprising two parts. Rectangular input signals are applied symmetrically and in opposite phase to each part, and fed to the emitters of the transistors through a respective input capacitor. The multivibrator is a relaxation oscillator consisting of two NPN transistors coupled through two capacitors, so that the input of one transistor is actuated through the respective capacitor, by the output of the other transistor. The input signals may be supplied by an identical multivibrator.

O Umted States Patent 1 1 3,569,864

[72] Inventor Igor Scherrer [56] References Cited C l m SwitzerlandUNITED STATES PATENTS [21] P 789305 2,572,698 10/1951 Canfora 331/51[221 PM 3,037,171 5/1962 Cerofolini 331/113x [451 Painted 1971 3,377,5694/1968 Mothersolc 331/145 [73] Assrgnee S. A. Ebauches N h g l, S it l dPrimary Examiner-John Kominski Assistant Examiner- Siegfried H. GrimmAttorney-Kenwood Ross [54] ASTABLE TRANSISTOR MULTIVIBRATOR ABSTRACT: Afrequency divider is formed by an astable g transistorised multivibratorof symmetrical construction com- [52] US. Cl 331/113, prising two parts.Rectangular input signals are applied sym- 307/225, 321/60, 325/39,325/201, 331/145, metrically and in opposite phase to each part, and fedto the 331/172 emitters of the transistors through a respective inputcapaci- [51] Int. Cl. H03k 3/282, tor. The multivibratoris a relaxationoscillator consisting of H03k 21/00 two NPN transistors coupled throughtwo capacitors, so that [50] Field 01' Search 331/51, 52, the input ofone transistor is actuated through the respective 11 (B), 145, 172, 173;321/60, 65, 69; 328/39, capacitor, by the output of the othertransistor. The input 201; 307/225 signals may be supplied by anidentical multivibrator.

ASTABLE TRANSISTOR MULTIVIBRATOR FREQUENCY.

DIVIDER v I The present invention relates to a frequency divider. Animportant class of frequency dividers uses the property that anyoscillator has, to a greater 'or less degree, or being Other objects andadvantages will emerge from the description which follows. t

The frequency divider accordingto the invention is characterized by thefact that it is constituted by an oscillator of symmetrical constructioninto each part of which are sentinput signals, these signals beingsymmetrical and of opposite phase, the whole being arranged so that theoscillator. is synchronized every half-period.

As a result, in the present frequency divider, the restoration intophase of the oscillator is effected at each half-period and not at eachwhole period of oscillation as in known frequency dividers. Through thisfact, all other things being equal, there is obtained double thedivision factor for the same safety of operation.

In order that the invention may be more fully understood one embodimentof a frequency divider according to the invention is described below,purely by way of illustrative but nonlimiting example, with reference tothe accompanying drawings, in which:

FIG. I shows the diagram of an astable transistorized mul tivibrator ofa frequency divider according to the invention; and

FIG. 2 is a diagram of the voltage as a function of time, of thefrequency divider of FIG. 1, for a division factor of 3.

Referring to the drawings, the astable multivibrator shown in FIG. 1 isa relaxation oscillator constituted by two active elements, here NPNtransistors T1 and T2, coupled to one another through capacities Cl andC2, so that the input of one i is actuated through the condenser C 1,and C2 respectively, by

the output of the other.

When one of the active elements is blocked, the other is conductive. Theswing from one state to the other is produced by the charge of thecondenser C1, and C2 respectively, through a resistance R1, and R2respectively, which cause the control voltage of the blocked element torise, that is to say the base-emitter voltage of the blocked transistorat the moment when it commences to conduct. The coupling of the twotransistors constitutes a positive reaction, the phenomenon iscumulative, that is to say that the increase in current in one of Y thetransistors causes a reduction in the other, and inversely. Theoscillation is hence very-rapid.

This multivibrator is synchronized by two rectangular signals shown inthe left-hand part of the figure, of opposite phase, applied to inputs.E and E These rectangular signals are differentiated by the inputcapacitators CEl and C52 respectively, and the short pulses, produced onthe right vertical sides of the input signals, are added to theexponential variation due to the charge of the capacities C2 and C1respectively, of the multivibrator.

The moment of swing, at the time when the base-emitter voltage of theblocked transistor reaches'the threshold of conduction, is determinedprecisely by the output pulse of the control signal, which ensuressynchronization of the multivibrator. There are collected, on thecollectors of the two transistors T and T namely at S, and S ,'signalsalso rectangular and of opposite phase, which enable the driving ofanother multivibrator identical with that which is shown.

The diagram of voltages of FIG. 2 indicates the applied signal at E, thevoltage at E, on the emitter of the transistor T then the base-emit ervoltage V N of the transistor T,

and finally the base-emitter voltage V N of the transistor It isespecially important to consider the base-emitter voltage of the blockedtransistor, for it is the positive pulse at the end of each half-periodwhich causes the, multivibrator to swing and thus replace it in phase.

It is seen, by referring to FIG. 2, that at each half-period, there is apulse V -V O for the blocked transistor and a pulse V -V 0 for thesaturated transistor.

These two effects are added, the first being more effective than thesecond, which leads to a very easy synchronization, the situationremaining the same for any odd number taken as factor of division.

It is to be noted that it is advantageous to apply the input pulses onthe transistor emitters rather than on their bases. In fact, in theblocked condition of the transistors, the pulses are only damped by theresistance R while in the saturated state of the transistors, the outputresistance of the transistor, seen from the emitter, is very weak, sothat the pulses are very strongly damped and have practically no effect.

Such a separation is no longer produced if the input is made on thebases, so that operation, although possible, is then more delicate.

I Finally, it should be pointed out that a division by an even number isnot possible.

. In fact, in that case, it would only be at the end of each period thatthe pulses would be of the desired polarity, while at the half-periodthe blocked transistor would receive a pulse V -V O and the saturatedtransistor a pulse V -V 0. The effect would hence be worse, for goodoperation, than the absence of pulses at the half-period.

It will be apparent that various changes and modifications may be madein the embodiment described without departing from the essential conceptof the invention as defined in scope by the appended claims.

Iclaim': I

1. An astable transistor multivibrator frequency divider comprising: I

a two-part relaxation oscillator of symmetrical construction for theapplication of rectangular input signals to each part, the input signalsbeing rectangular signals applied symmetrically and in opposite phase tothe emitters of the transistors, the two transistors being coupledthrough two capacitors, so that the input of one transistor is actuatedthrough the respective capacitor by the output of the other transistor,the oscillator being synchronized every half-period. 2. The frequencydivider according to claim 1, the mulferentiate the rectangular inputsignals.

2. The frequency divider according to claim 1, the multivibratorincluding two input capacitators arranged to differentiate therectangular input signals.